<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container{
            display: flex;
        }
        .left,.right{
            width: 200px;
        }

        .main{
            flex: 1;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="left" style="border: 1px solid black">left Sidebar</div>
        <div class="main" style="border: 1px solid blue;">main content</div>
        <div class="right" style="border: 1px solid red;">right Sidebar</div>
    </div>
</body>
</html>